The present invention relates generally to hydroforming methods and die assemblies, and more particularly to a hydroforming method and die assembly for hydroforming a tubular metal blank in a manner which avoids the need for a pre-crush operation for inserting the blank into the die cavity.
Hydroforming methods are commonly known as a means for shaping a tubular metal blank having a circular cross section into a tubular component having a predetermined desired configuration. In particular, a typical hydroforming operation involves the placement of a tubular metal blank having a circular cross section into a die cavity of a hydroforming assembly and providing high pressure fluid to the interior of the blank to cause the blank to expand outwardly into conformity with the surfaces defining the die cavity. More particularly, the opposite longitudinal ends of the tubular metal blank are sealed by hydraulic rams, and high pressure hydroforming fluid is provided through a port formed in one of the rains to expand the tubular blank.
Typically, the tubular blank having the circular cross-section is roll formed from sheet metal into its initial configuration. The roll formed tubular blank must then he placed into the hydroforming die cavity, typically having a boxed, rectangular, or irregular cross-section. Because the circumference of a circular tubular blank that would fit easily into the die cavity is significantly less than the circumference or cross-sectional perimeter of the surfaces defining the die cavity, significant expansion of the blank would be necessary to conform the blank to the die cavity. Such significant expansion may cause significant wall thinning of the tubular blank, so that a blank of substantial initial wall thickness would be required. Moreover, if such significant expansion is required, it becomes more difficult for the blank to conform into the corners within the die cavity. To minimize the amount of expansion necessary and to provide a tubular blank that has a circumference that initially conforms more closely to the cross sectional perimeter of the die cavity, it has been a conventional practice to provide a tubular blank having circular cross-sectional diameter that is greater than the width of the die cavity and to crush the tube diametrically in a pre-crush station to enable the tube to be initially placed into the relatively narrow die cavity. The pre-crush operation, however, is costly in that it requires dedicated machinery and is time consuming.
It is object of the present invention, therefore, to eliminate the need for the costly pre-crush operation while using a tubular blank that conforms better to the contours of the die cavity. This object is achieved in accordance with the principles of the present invention by a method of forming an elongated tubular metal member having a cross-sectional configuration such that it includes a first cross-sectional dimension which is greater than a second cross-sectional dimension orthagonal to the first cross-sectional dimension along an extent thereof. The method utilizes a die assembly having first and second die structures having surfaces cooperable to define a die cavity having a first cross-sectional dimension which is greater than a second cross-sectional dimension generally orthagonal to the first cross-sectional dimension. The method comprises i) roll-forming sheet metal to form a tubular metal blank having an oval cross-section, the oval cross-section including a major axis along a greater diameter thereof and a minor axis along a smaller diameter thereof, the major and minor axes being generally orthagonal to one another; ii) placing the tubular metal blank into the second die structure, the second die structure being constructed and arranged to receive the tubular metal blank having the oval cross-section without distorting the tubular metal blank from its oval cross-section, the tubular metal blank being placed into the second die structure such that the major axis of the oval cross-section thereof extends in generally the same direction as the first cross-sectional dimension when the first and second die structures cooperate to form the die cavity and such that the minor axis of the oval cross-section thereof extends in generally the same direction as the second cross-sectional dimension of the die cavity when the first and second die structures cooperate to form the die cavity; iii) engaging opposite ends of the tubular metal blank with tube-end engaging structures so as to substantially seal opposite ends of the tubular metal blank; and iv) injecting fluid under pressure into the tubular metal blank placed in the die cavity to expand the tubular metal blank into conformity with the surfaces defining the (die cavity.
The object is also achieved in accordance with the principle of the present invention by an apparatus for forming a tubular metal blank into an elongated tubular metal member having a substantially box-shaped transverse cross-section along an extent thereof. The apparatus comprises a die assembly having an internal die surface defining a die cavity, the die cavity having a substantially box-shaped surface configuration and being constructed and arranged to receive the tubular metal blank having a generally oval cross-section. Clamping structures are positioned on opposite ends of the die cavity and constructed and arranged to securely clamp spaced-apart portions of the tubular metal blank. The clamping structures present clamping surfaces defining a generally oval surface configuration generally conforming to a generally oval outer peripheral surface of the tubular metal blank. The apparatus further comprises tube-end engaging structure constructed and arranged to engage and substantially seal opposite ends of the tubular metal blank, the tube-end engaging structure presenting a generally oval outer surface configuration conforming to a generally oval inner peripheral surface of the tubular metal blank.
The object is also achieved in accordance with the principles of the present invention by providing a method of forming an elongated tubular metal member, the elongated tubular metal member being formed in a die cavity having surfaces constructed and arranged to provide the die cavity with a shape generally corresponding to a shape of the of the elongated tubular member. The cross-section of the elongated tubular member and hence of the die cavity has a relatively larger dimension thereof transverse to a relatively smaller dimension thereof. The method comprises: i) placing a tubular metal blank having a generally oval cross-section into the die cavity and orienting the tubular metal blank such that a relatively larger cross-sectional dimension of the generally oval cross-section extends generally in a direction of the relatively larger cross-sectional dimension of the die cavity and such that a relatively smaller cross-sectional dimension of the generally oval cross-section extends generally in a direction of the relatively smaller cross-sectional dimension of the die cavity; ii) engaging and sealing opposite ends of the tubular metal blank; and iii) injecting fluid under pressure into the tubular metal blank so as to expand the tubular metal blank into conformity with the surfaces defining the die cavity and thereby transform the tubular metal blank into the elongated tubular metal member.
Other objects and advantages of the present invention will be realized in accordance with the following detailed description, appended drawings and claims.